This invention relates to frequency discriminators utilizing surface wave devices and more particularly to frequency discriminators utilizing a pair of surface wave devices each having a single transducer.
Surface wave devices have found a number of applications as frequency selective or responsive devices such as in filters, frequency discriminators, and the like. Such devices normally comprise one or more interdigital transducers disposed on a substrate of piezoelectric material such as lithium niobate, lithium tantalate, PZT, quartz, zinc oxide, zinc sulfide, or cadmium sulfide. Of the various possible piezoelectric materials, lithium niobate is presently preferred, however, depending upon the application and the frequencies of interest, other materials may be used as well and may in some cases be preferred. Surface wave devices possess a number of advantages over frequency responsive circuits constructed of discrete components such as small size, compatability with integrated circuits, relatively invariant characteristics, bulk fabrication, and the like.
Prior art frequency discriminators utilizing surface wave devices have generally included transmitting and receiving transducers disposed on a piezoelectric substrate. Such devices, however, have parasitic responses due to various parasitic effects such as side lobe responses, bulk wave coupling, capacitive and inductive coupling, and the like. Such parasitic effects deleteriously affect the performance of such prior art frequency discriminators. Furthermore, prior art frequency discriminators utilizing transmitting and receiving transducers require relatively complex design and fabrication techniques and have a relatively high insertion loss or low efficiency.
Attempts to circumvent the disadvantages of frequency discriminators utilizing transmitting and receiving transducers have been generally unsuccessful. Some prior art attempts involve the use of designs including surface wave devices with single transducers, however, these prior art techniques have also resulted in transducers with low efficiency and inadequate or deleterious performance.